Hadrons are composite particles made of quarks. The strong force, mediated by gluons, holds quarks together inside hadrons. The two main types of hadrons are baryons, made of three quarks, and mesons, made of a quark and an antiquark. Hadrons are classified according to their spin and parity.
Who proposed the theory of quarks?
What is the strong nuclear force mediated by?
What are the two main classes of hadrons?